

public class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 }

class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null) return null;
        if(head.next == null) return head;

        ListNode cur = head.next;
        head.next = null;

        while(cur != null){
            ListNode curNext = cur.next;
            cur.next = head;
            head = cur;
            cur = curNext;
        }
        return head;

    }
}